Showing papers by "Lidija Andric published in 2015"

Single photon simultaneous K-shell ionization and K-shell excitation. I. Theoretical model applied to the interpretation of experimental results on H2O.

Abstract: We present in detail a theoretical model that provides absolute cross sections for simultaneous core-ionization core-excitation (K−2V ) and compare its predictions with experimental results obtained on the water molecule after photoionization by synchrotron radiation. Two resonances of different symmetries are assigned in the main K−2V peak and comparable contributions from monopolar (direct shake-up) and dipolar (conjugate shake-up) core-valence excitations are identified. The main peak is observed with a much greater width than the total experimental resolution. This broadening is the signature of nuclear dynamics.

Single photon simultaneous K-shell ionization and K-shell excitation. II. Specificities of hollow nitrogen molecular ions

Abstract: The formalism developed in the companion Paper I is used here for the interpretation of spectra obtained recently on the nitrogen molecule. Double core-hole ionization K−2 and core ionization-core excitation K−2V processes have been observed by coincidence electron spectroscopy after ionization by synchrotron radiation at different photon energies. Theoretical and experimental cross sections reported on an absolute scale are in satisfactory agreement. The evolution with photon energy of the relative contribution of shake-up and conjugate shake-up processes is discussed. The first main resonance in the K−2V spectrum is assigned to a K−2π∗ state mainly populated by the 1s→ lowest unoccupied molecular orbital dipolar excitation, as it is in the K−1V NEXAFS (Near-Edge X-ray Absorption Fine Structure) signals. Closer to the K−2 threshold Rydberg resonances have been also identified, and among them a K−2σ∗ resonance characterized by a large amount of 2s/2p hybridization, and double K−2(2σ∗/1π/3σ)−11π∗2 shake-up...

Valence Auger decay following 3 s photoionization in potassium

Abstract: We have studied photoionization in the inner valence $3s$ subshell of K and the spectroscopic properties of the two $3{s}^{\ensuremath{-}1}\phantom{\rule{0.28em}{0ex}}(^{1}S)$ and $(^{3}S)$ resulting states. Similar to the Rb and Cs cases, the lifetime widths of the $(^{1}S)$ and $(^{3}S)$ states are found to be markedly different, due to the electron correlation effects. The main part of the study deals with the subsequent Auger decay of the $3{s}^{\ensuremath{-}1}$ states, which have the particularity to involve low energy $(\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$ Auger electrons. A magnetic bottle spectrometer with a multicoincidence technique has been used to observe and filter the Auger spectra with respect to the ${\mathrm{K}}^{2+}$ final state. The evolution of these Auger spectra has been investigated near the ionization threshold. They show strong post-collision interaction (PCI) effects, which are well reproduced by semiclassical and eikonal models. They reveal the importance of the photoelectron--Auger-electron interaction associated with these low energy Auger electrons.

Auger decay paths of mercury 5 p and 4 f vacancies revealed by multielectron spectroscopy

Abstract: Single and double Auger processes following ionization of $4f$ and $5p$ inner shells have been studied using multielectron coincidence spectroscopy. Coincidence technique enables us to resolve state by state all single and double Auger paths with a resolution better than the lifetime broadening. Drastic step-to-step decay lifetime changes are observed and reported as Coster-Kronig transition takes place either in the first $(5p)$ or in the second $(4f)$ step of the Auger cascade. Relativistic ab initio theory has been used to predict and interpret the experimental observations.

Auger decay of core valence double photoionized states in atomic mercury

Abstract: Multielectron coincidence spectroscopy has been used to study the Auger decay following the core (4f)—valence (5d, 6s) double photoionization of atomic mercury. Multiconfiguration Dirac–Fock calculations have been performed to predict the transition energies and populations of the triple ionized Auger final states. A good agreement between the experiment and simulated spectra is found.

Post-collision interaction in Potassium 3s photoionization

Abstract: The post-collision interaction (PCI) distortion of the Auger electron line shapes after K 3s photoionization is revealed in coincidence measurements and confirmed by calculations.

Single photon core ionization with core excitation: A new spectroscopic tool

Abstract: The simultaneous core ionization and core excitation process (or K-2V process) induced by absorption of a single photon provides the basis of a new spectroscopy that offers both advantages of X-ray Photoelectron Spectroscopy (XPS) and near-edge x-ray absorption fine structures (NEXAFS) spectroscopy